Anti-pad for a printed circuit board

ABSTRACT

A printed circuit board includes a substrate having a plurality of stacked circuit board layers. The substrate has a top surface and a bottom surface. The printed circuit board includes a signal contact on the substrate. The signal contact has a signal via and a signal trace extending from the signal via. The signal via extends between the top surface and the bottom surface along a via axis. The printed circuit board includes an anti-pad around the signal via extending through the substrate along the via axis. The anti-pad extends between the top surface and the bottom surface. The anti-pad has a first width at the top surface and the lower anti-pad has a second width at the bottom surface different than the first width.

BACKGROUND OF THE INVENTION

The subject matter herein relates generally to printed circuit boards.

In general, a printed circuit board (“PCB”) refers to a component ontowhich various elements are mounted or electrically connected throughintegrated wiring. PCBs generally provide a reliable and economicalmeans of interconnecting electrical signals between system components.With technological development, the PCBs are being manufactured to havegreater numbers of layers to reduce the PCB board size whileaccommodating greater components for miniaturization and highspeedapplications. Multilayer PCBs are manufactured to include multiplelayers of insulating material upon which patterns of electricalconductors are formed. In addition to a pattern of conductive traces onthe PCB, a patterned array of metal-filled through-holes, or vias, maybe formed to allow for layer-to-layer interconnections between variousconductive features. Anti-pads are provided that surround the vias andprovide separation between the vias and other conductive layers of thePCB. The anti-pads affect impedance of the signal transmission linethrough the via. A signal trace extends from each signal via. Some knownPCBs vary the width of the signal trace to optimize electricalperformance. However, for high layer PCBs signal impedance control isproblematic. Additionally, impedance control provided by the signaltrace occupies valuable real estate on the substrate, which may limitpositioning of other signal vias and ground vias.

A need remains for a PCB having improved impedance control.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a printed circuit board is provided. The printedcircuit board includes a substrate having a plurality of stacked circuitboard layers. The substrate has a top surface and a bottom surface. Theprinted circuit board includes a signal contact on the substrate. Thesignal contact has a signal via and a signal trace extending from thesignal via. The signal via extends between the top surface and thebottom surface along a via axis. The printed circuit board includes ananti-pad around the signal via extending through the substrate along thevia axis. The anti-pad extends between the top surface and the bottomsurface. The anti-pad has a first width at the top surface and the loweranti-pad has a second width at the bottom surface different than thefirst width.

In another embodiment, a printed circuit board is provided. The printedcircuit board includes a substrate having a top surface and a bottomsurface. The substrate has a plurality of stacked circuit board layersincluding an upper board stack at the top surface and a lower boardstack at the bottom surface. The printed circuit board includes a signalcontact on the substrate. The signal contact has a signal via and asignal trace extending from the signal via. The signal via includes anupper signal via through the upper board stack and a lower via throughthe lower board stack. The upper via and the lower via are aligned alonga via axis. The printed circuit board includes an anti-pad around thesignal via extending through the substrate along the via axis. Theanti-pad has an upper anti-pad aligned with the upper via and a loweranti-pad aligned with the lower via. the upper anti-pad has a firstwidth and the lower anti-pad has a second width different than the firstwidth.

In a further embodiment, an electrical connector assembly is provided.The electrical connector includes a housing holding signal contacts andground contacts. The housing has a mounting end. The electricalconnector assembly includes a printed circuit board supporting theelectrical connector. The printed circuit board includes a substratehaving a plurality of stacked circuit board layers. The substrate has atop surface and a bottom surface. The mounting end of the electricalconnector are mounted to the top surface of the substrate. The printedcircuit board includes signal contacts and ground contacts. The signalcontacts of the printed circuit board are electrically coupled tocorresponding signal contacts of the electrical connector. The groundcontacts of the printed circuit board are electrically coupled tocorresponding ground contacts of the electrical connector. Each signalcontact has a signal via extending between the top surface and thebottom surface along a via axis and a signal trace extending from thesignal via. The printed circuit board includes anti-pads around thecorresponding signal vias. The anti-pads extend through the substratealong the corresponding via axis between the top surface and the bottomsurface. The anti-pads have stepped profiles through the substrate withvarying widths along the heights of the anti-pads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an electrical connector assembly including aprinted circuit board (PCB) in accordance with an exemplary embodiment.

FIG. 2 is a bottom, perspective view of the PCB in accordance with anexemplary embodiment.

FIG. 3 is a bottom view of a portion of the PCB in accordance with anexemplary embodiment.

FIG. 4 is a bottom view of a portion of the PCB in accordance with anexemplary embodiment.

FIG. 5 is a cross-sectional view of a portion of the PCB in accordancewith an exemplary embodiment.

FIG. 6 is a cross-sectional view of a portion of the PCB in accordancewith an exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a side view of an electrical connector assembly 100 includinga printed circuit board (PCB) 110 in accordance with an exemplaryembodiment. The electrical connector assembly 100 includes an electricalconnector 102 having a housing 104 holding signal contacts 106 andground contacts 108. The signal contacts 106 and the ground contacts 108have mating ends configured to be mated with a mating electricalconnector. The signal contacts 106 and the ground contacts 108 havemounting ends configured to be mounted to the PCB 110. For example, themounting ends of the signal contacts 106 and the ground contacts 108 maybe defined by compliant pins, such as eye of the needle pins, configuredto be press-fit into plated vias of the PCB 110. In other variousembodiments, the mounting ends of the signal contacts 106 and/or theground contacts 108 may be other types, such as solder tails.

The PCB 110 supports the electrical connector 102. The PCB 110 includesa substrate 112 having a top surface 114 and a bottom surface 116. Thesubstrate 112 has a plurality of stacked circuit board layers formingthe substrate 112. The substrate 112 may include any number of circuitboard layers and, in an exemplary embodiment, includes a high number ofcircuit board layers, such as greater than ten circuit board layers. Amounting end 118 of the electrical connector 102 is mounted to the topsurface 114 of the substrate 112.

The PCB 110 includes signal contacts 120 and ground contacts 122 (shownin phantom). The signal contacts 120 of the PCB 110 are electricallyconnected to corresponding signal contacts 106 of the electricalconnector 102. The ground contacts 122 of the PCB 110 are electricallyconnected to corresponding ground contacts 108 of the electricalconnector 102. Each signal contact 120 includes a signal via 124extending between the top surface 114 and the bottom surface 116 along avia axis 126. The signal via 124 receives the signal contact 106 of theelectrical connector 102. In an exemplary embodiment, the signal via 124is plated to electrically connect to the signal contact 106 of theelectrical connector 102. Each ground contact 122 includes a ground via128 extending between the top surface 114 and the bottom surface 116. Inan exemplary embodiment, the ground via 128 is plated to electricallyconnect to the ground contact 108 of the electrical connector 102.

In an exemplary embodiment, the PCB 110 includes anti-pads 130 (shown inphantom) around the corresponding signal vias 124. The anti-pads 130 arevoid areas or keep-out areas around the signal via 124 that are devoidof the ground contacts 122 and ground planes along various layers of thesubstrate 112. The anti-pads 130 extend through the substrate 112 alongthe corresponding via axis 126 between the top surface 114 and thebottom surface 116. In the illustrated embodiment, each anti-pad 130surrounds a corresponding signal via 124. In alternative embodiments,multiple signal vias 124 may be provided within a corresponding anti-pad130. For example, a pair of signal vias 124 may be arranged within asingle anti-pad 130.

In an exemplary embodiment, each anti-pad 130 has a stepped profilethrough the substrate 112 with a varying width along the height of theanti-pad 130. For example, each anti-pad 130 may have a first width atthe top surface 114 and a second width at the bottom surface 116 that isdifferent than the first width. While the anti-pad 130 is illustrated ashaving a single step (for example, areas having two different widths),it is realized that the anti-pad 130 may have multiple steps inalternative embodiments.

The stepped structure of the anti-pad 130 varies the distance or spacingbetween the signal via 124 and ground planes and/or the ground via 128,which affects impedance of the signal transmission lines through thesignal via 124. The ground via 128 is positioned at variable distancesfrom the anti-pad 130 along the height. For example, the ground via 128is positioned a first distance from the anti-pad 130 at the top surface114 and is positioned a second distance from the anti-pad 130 at thebottom surface 116 that is different than the first distance.

FIG. 2 is a bottom, perspective view of the PCB 110 in accordance withan exemplary embodiment. FIG. 2 illustrates the signal contacts 120 andthe ground contacts 122 at the bottom surface 116 of the substrate 112.In an exemplary embodiment, the PCB 110 includes one or more groundplanes 132, such as at one or more layers of the substrate 112. In anexemplary embodiment, the PCB 110 includes one of the ground planes 132at the bottom surface 116. The ground plane 132 is electricallyconnected to the ground contacts 122. In an exemplary embodiment, eachground contact 122 includes a ground pad 134 electrically connected tothe ground plane 132. The ground plane 132 electrically connects each ofthe ground contacts 122.

In an exemplary embodiment, each signal contact 120 includes a signalpad 136 and a signal trace 138. In the illustrated embodiment, thesignal pad 136 and the signal trace 138 are provided at the bottomsurface 116. The signal pad 136 and the signal trace 138 may be providedat the top surface 114 or may be provided at an inner layer of the stackof circuit board layers of the substrate 112 in other variousembodiments. The signal trace 138 is routed along the correspondinglayer of the substrate 112 to another location remote from the signalvia 124. In an exemplary embodiment, the signal trace 138 has a traceanti-pad 140 extending along the signal trace 138 on the correspondinglayer of the substrate 112 to isolate the signal trace 138 from theground plane 132. The trace anti-pad 140 is different from the anti-pad130 of the signal via 124 in that the trace anti-pad 140 is onlyprovided on a single layer of the substrate 112 rather than extendingentirely through the substrate 112.

FIG. 3 is a bottom view of a portion of the PCB 110 in accordance withan exemplary embodiment. FIG. 3 illustrates the signal via 124 and theanti-pad 130 around the signal via 124. In the illustrated embodiment,the signal via 124 is cylindrical. The signal via 124 is defined byplating 142 of a through hole 144 extending through the substrate 112.The through hole 144 is configured to receive the signal contact 106(shown in FIG. 1) such that the signal contact 106 directly engages theplating 142 to electrically connect the signal contact 106 with thesignal via 124.

The anti-pad 130 completely surrounds the signal via 124. In anexemplary embodiment, the anti-pad 130 is coincident with the via axis126. For example, a centroid of the anti-pad 130 is coincident with thevia axis 126. In the illustrated embodiment, the anti-pad 130 isparallelepiped. The anti-pad 130 may have a rectangular cross-section.Optionally, the anti-pad 130 may have a square cross-section. Theanti-pad 130 may have other shapes in alternative embodiments. In anexemplary embodiment, the anti-pad 130 has a variable width. Forexample, the anti-pad 130 has a first width 150 along a portion thereofand a second width 152 along a different portion thereof. In theillustrated embodiment, the first width 150 is narrower than the secondwidth 152. The anti-pad 130 may have the first width 150 along one ormore layers of the substrate 112 and the second width 152 along one ormore layers of the substrate 112.

FIG. 4 is a bottom view of a portion of the PCB 110 in accordance withan exemplary embodiment. FIG. 4 illustrates the anti-pad 130 as astamped, cylindrical structure. The anti-pad 130 has a circularcross-section. In alternative embodiments, the anti-pad 130 may haveother shapes, such as an oval cross-section. In an exemplary embodiment,the anti-pad 130 has a variable width (for example, diameter). Forexample, the anti-pad 130 has a first width 154 along a portion thereofand a second width 156 along a different portion thereof. In theillustrated embodiment, the first width 154 is narrower than the secondwidth 156. The anti-pad 130 may have the first width 154 along one ormore layers of the substrate 112 and the second width 156 along one ormore layers of the substrate 112.

FIG. 5 is a cross-sectional view of a portion of the PCB 110 inaccordance with an exemplary embodiment. FIG. 5 illustrates the signalvia 124 and the anti-pad 130 around the signal via 124 extending throughthe stack of circuit board layers 160. The stack of circuit board layers160 includes an upper circuit board layer 162 at the top surface 114 anda lower circuit board layer 164 at the bottom surface 116. The stack ofcircuit board layers 160 includes intermediate circuit board layers 166between the upper and lower circuit board layers 162, 164.

The anti-pad 130 is a stepped structure through the stack of circuitboard layers 160 surrounding the signal via 124. The shape of theanti-pad 130 controls the impedance of the signal transmission linesthrough the signal via 124 by varying the distance or spacing betweenthe signal via 124 and the ground planes 132 or other ground structureswithin the substrate 112. For example, the widths of the variousportions of the anti-pad 130 and/or the heights of the various portionsof the anti-pad 130 may be selected at the design phase of manufacturingthe PCB 110 to control the impedance of the signal transmission line.Greater impedance control of the PCB 110 is provided at the anti-padarea of the substrate 112, as opposed to providing impedance controlalong the signal trace 138 using trace anti-pads as is typical ofconventional PCB designs, which occupies and affects a larger footprintalong the substrate 112.

In an exemplary embodiment, the substrate 112 includes an upper boardstack 170 having a plurality of the circuit board layers 160 and a lowerboard stack 172 having a plurality of the circuit board layers 160. Theupper board stack 170 includes the upper circuit board layer 162. Thelower board stack 172 includes the lower circuit board layer 164. Theanti-pad 130 passes through the upper board stack 170 and the lowerboard stack 172. The anti-pad 130 is stepped at the interface betweenthe upper board stack 170 and the lower board stack 172 such that theanti-pad 130 has the first width 150 through the upper board stack 170and the second width 152 through the lower board stack 172. In variousembodiments, the substrate 112 may include additional board stacks, suchas an intermediate board stack between the upper board stack 170 and thelower board stack 172, wherein the anti-pad 130 has a different widththrough the intermediate board stack(s).

The signal via 124 extends between corresponding signal pads 136 on theupper and lower circuit board layers 162, 164 at the top surface 114 andthe bottom surface 116, respectively. The signal via 124 extends alongthe via axis 126. In an exemplary embodiment, a centroid axis 168 of theanti-pad 130 is coincident with the via axis 126. The signal trace 138extends from the signal pad 136 on the lower circuit board layer 164 atthe bottom surface 116 of the substrate 112; however, the signal trace138 may extend from the signal pad 136 on the upper circuit board layer162 or from an intermediate circuit board layer 166 in alternativeembodiments. In an exemplary embodiment, one or more of the circuitboard layers 160 include ground planes 132. However, the ground planes132 do not extend into the anti-pad 130. The anti-pad 130 is devoid ofground planes 132.

The anti-pad 130 extends through the stack of circuit board layers 160between the top surface 114 and the bottom surface 116. The anti-pad 130is manufactured from a dielectric material, such as a glass fiberreinforced epoxy resin. In various embodiments, the anti-pad 130 ismanufactured from an FR4 material. In other various embodiments, theanti-pad 130 may be manufactured from a polyamide material, a PTFEmaterial, or another dielectric material. The anti-pad 130 may bemanufactured from the same materials used to manufacture other areas ofthe circuit board layers 160 of the substrate 112.

In an exemplary embodiment, the anti-pad 130 includes an upper anti-pad180 at the top surface 114 and a lower anti-pad 182 at the bottomsurface 116. The upper anti-pad 180 extends through the upper boardstack 170, including the upper circuit board layer 162. The loweranti-pad 182 extends through the lower board stack 172 including thelower circuit board layer 164. The upper anti-pad 180 has the firstwidth 150 and the lower anti-pad 182 has the second width 152. In theillustrated embodiment, the second width 152 is wider than the firstwidth 150. The upper anti-pad 180 has a first height 184 and the loweranti-pad 182 has a second height 186. The heights 184, 186 are definedby the thicknesses of the circuit board layers 160 and the number ofcircuit board layers 160 in the upper and lower anti-pads 180, 182,respectively. In the illustrated embodiment, the first height 184 istaller than the second height 186; however, the second height 186 may betaller than the first height 184 or the first and second heights 184,186 may be equal in alternative embodiments. The first height 184 andthe first width 150 are selected for impedance tuning of the signalcontact 120. The second height 186 and the second width 152 are selectedfor impedance tuning of the signal contact 120.

FIG. 6 is a cross-sectional view of a portion of the PCB 110 inaccordance with an exemplary embodiment. FIG. 6 illustrates the anti-pad130 having the upper anti-pad 180, the lower anti-pad 182 and anintermediate anti-pad 188 between the upper anti-pad 180 and the loweranti-pad 182. The intermediate anti-pad 188 is located at anintermediate board stack 174 located between the upper board stack 170and the lower board stack 172. The intermediate anti-pad 188 has a thirdwidth 190 different than the first width 150 and different from thesecond width 152. The anti-pad 130 is stepped between the upper anti-pad180 and the intermediate anti-pad 188 and is stepped between theintermediate anti-pad 188 and the lower anti-pad 182. In the illustratedembodiment, the third width 190 is narrower than the second width 152and wider than the first width 150. However, other arrangements arepossible in alternative embodiments, such as with the third width 190being the narrowest portion of the anti-pad 130 or the widest portion ofthe anti-pad 130. The anti-pad 130 may include additional intermediateanti-pad portions having different widths then adjacent anti-padportions.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. Dimensions, types of materials,orientations of the various components, and the number and positions ofthe various components described herein are intended to defineparameters of certain embodiments, and are by no means limiting and aremerely exemplary embodiments. Many other embodiments and modificationswithin the spirit and scope of the claims will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

1. A printed circuit board comprising: a substrate having a plurality ofstacked circuit board layers, the substrate having a top surface and abottom surface; a signal contact on the substrate, the signal contacthaving a signal via and a signal trace extending from the signal via,the signal via extending between the top surface and the bottom surfacealong a via axis; and an anti-pad around the signal via extendingthrough the substrate along the via axis, the anti-pad extending betweenthe top surface and the bottom surface, the anti-pad having a firstwidth at the top surface, the anti-pad having a second width at thebottom surface different than the first width, the anti-pad including anupper anti-pad at the top surface having the first width, a loweranti-pad at the bottom surface having the second width, and anintermediate anti-pad between the upper anti-pad and the lower anti-pad,the intermediate anti-pad having a third width different than the firstwidth and different than the second width, the upper anti-pad comprisingat least two of the circuit board layers, the lower anti-pad comprisingat least two of the circuit board layers, the intermediate anti-padcomprising at least two of the circuit board layers.
 2. The printedcircuit board of claim 1, wherein the anti-pad has a stepped profilethrough the substrate with a varying width along a height of theanti-pad.
 3. (canceled)
 4. (canceled)
 5. The printed circuit board ofclaim 1, wherein the upper anti-pad has a first height and the loweranti-pad has a second height different than the first height.
 6. Theprinted circuit board of claim 5, wherein the first height and the firstwidth are selected based on the second height and the second width forimpedance tuning of the signal contact.
 7. The printed circuit board ofclaim 1, wherein the substrate includes an upper board stack having aplurality of the circuit board layers and a lower board stack having aplurality of the circuit board layers, the anti-pad having the firstwidth through the upper board stack and the anti-pad having the secondwidth through the lower board stack.
 8. (canceled)
 9. The printedcircuit board of claim 1, wherein the anti-pad is cylindrical.
 10. Theprinted circuit board of claim 1, wherein the anti-pad isparallelepiped.
 11. The printed circuit board of claim 1, furthercomprising a ground contact having a ground via extending through thesubstrate between the top surface and the bottom surface, the ground viapositioned a first distance from the anti-pad at the top surface, theground contact positioned a second distance from the anti-pad at thebottom surface, the second distance being different than the firstdistance.
 12. A printed circuit board comprising: a substrate having atop surface and a bottom surface, the substrate having a plurality ofstacked circuit board layers including an upper board stack at the topsurface and a lower board stack at the bottom surface; a signal contacton the substrate, the signal contact having a signal via and a signaltrace extending from the signal via, the signal via including an uppervia through the upper board stack and a lower via through the lowerboard stack, the upper via and the lower via being aligned along a viaaxis; and an anti-pad around the signal via extending through thesubstrate along the via axis, the anti-pad having an upper anti-padaligned with the upper via and a lower anti-pad aligned with the lowervia, the upper anti-pad having a first width, the lower anti-pad havinga second width different than the first width, wherein the anti-padincludes an intermediate anti-pad between the upper anti-pad and thelower anti-pad, the intermediate anti-pad having a third width differentthan the first width and different than the second width, theintermediate anti-pad comprising at least two of the circuit boardlayers.
 13. The printed circuit board of claim 12, wherein the anti-padhas a stepped profile through the substrate with a varying width along aheight of the anti-pad.
 14. (canceled)
 15. The printed circuit board ofclaim 12, wherein the upper anti-pad has a first height and the loweranti-pad has a second height different than the first height.
 16. Theprinted circuit board of claim 12, wherein the substrate includes anupper board stack having a plurality of the circuit board layers and alower board stack having a plurality of the circuit board layers, theupper anti-pad extending through the upper board stack and the loweranti-pad extending through the lower board stack.
 17. The printedcircuit board of claim 12, further comprising a ground contact having aground via extending through the substrate between the top surface andthe bottom surface, the ground via positioned a first distance from theanti-pad at the top surface, the ground contact positioned a seconddistance from the anti-pad at the bottom surface, the second distancebeing different than the first distance.
 18. An electrical connectorassembly comprising: an electrical connector including a housing holdingsignal contacts and ground contacts, the housing having a mounting end;and a printed circuit board supporting the electrical connector, theprinted circuit board including a substrate having a plurality ofstacked circuit board layers, the substrate having a top surface and abottom surface, the mounting end of the electrical connector beingmounted to the top surface of the substrate, the printed circuit boardincluding signal contacts and ground contacts, the signal contacts ofthe printed circuit board being electrically coupled to correspondingsignal contacts of the electrical connector, the ground contacts of theprinted circuit board being electrically coupled to corresponding groundcontacts of the electrical connector, each signal contact having asignal via extending between the top surface and the bottom surfacealong a via axis and a signal trace extending from the signal via, theprinted circuit board including anti-pads around the correspondingsignal vias, the anti-pads extending through the substrate along thecorresponding via axis between the top surface and the bottom surface,the anti-pads having stepped profiles through the substrate with varyingwidths along the heights of the anti-pads, wherein the anti-pad includesan upper anti-pad at the top surface having the first width, a loweranti-pad at the bottom surface having the second width, and anintermediate anti-pad between the upper anti-pad and the lower anti-padhaving a third width different than the first width and different thanthe second width.
 19. The electrical connector assembly of claim 18,wherein each anti-pad has a first width at the top surface and a secondwidth at the bottom surface different than the first width.
 20. Theelectrical connector assembly of claim 18, wherein each of thecorresponding ground contacts includes a ground via extending betweenthe top surface and the bottom surface, the ground via positioned afirst distance from the anti-pad at the top surface, the ground contactpositioned a second distance from the anti-pad at the bottom surface,the second distance being different than the first distance. 21.(canceled)
 22. The electrical connector assembly of claim 18, whereinthe anti-pads each having a centroid axis coincident with thecorresponding via axis along a height of the substrate between the topsurface and the bottom surface.
 23. The printed circuit board of claim1, wherein the anti-pad has a centroid axis coincident with the via axisalong a height of the substrate between the top surface and the bottomsurface.
 24. The printed circuit board of claim 12, wherein the anti-padhas a centroid axis coincident with the via axis through the upper boardstack and through the lower board stack